This invention relates to an improved method for hydro-dealkylation of alkyl aromatic hydrocarbons and more particularly it relates to an improved method for producing useful compounds such as benzene and the like by catalytic hydro-dealkylation of alkyl aromatic hydrocarbons using a catalyst mainly composed of zeolite a part of exchangeable cations of which are exchanged with hydrogen ions.
Hitherto, for producing useful compounds such as benzene from alkyl aromatic hydrocarbons there has been widely used a method which comprises catalytically hydro-dealkylating the alkyl aromatic hydrocarbons using a catalyst, e.g., chromia or molybdena carried on alumina generally at a temperature of about 600.degree. C.
However, this method has the difficulties that high temperatures are required for increasing productivity because said catalysts have no sufficient activity and use of high temperatures causes very serious deterioration of the catalysts. Furthermore, it has been generally known that various cation exchange zeolites possess catalytic activity for dealkylation reaction and disproportionation reaction of aromatic hydrocarbons. For example, there has been proposed a method for carrying out these reactions using, as catalysts, zeolites which are almost completely ion-exchanged with hydrogen ion which is a non-metallic cation. (See Japanese Patent Publication No. 25967/68). However, although zeolites which are cation exchanged with hydrogen ion by 50% or more have higher dealkylation activity as compared with conventional catalysts, they also have high disproportionation activity and so they are inferior in selectivity to provide undesired by-products and moreover they have high deterioration rate caused by deposition of coke.
As the result of the inventors' intensive researches to overcome these defects, it has been found that useful compounds such as benzene and the like can be obtained in high yield and selectivity by catalytic hydro-dealkylation of alkyl aromatic hydrocarbons using a zeolite having a specific hydrogen ion exchange ratio in the presence of hydrogen at a temperature of a specific range and that zeolites which contain a certain kind of metals as cations besides hydrogen ion are higher in stability and less in deterioration with time as hydro-dealkylation catalysts.